Process for encapsulating a waste material

ABSTRACT

Sludges and slurries, e.g., oil, grease or paint based, are encapsulated into fly ash or similar particulate material by adding solvents to effect the encapsulation and absorption of the sludge. Subsequently, the particulate material is heated to remove the solvent, leaving a dry powder which may then be used as a filler for various applications, including production of breeze blocks.

BACKGROUND OF THE INVENTION

This invention relates to a process and apparatus for encapsulating ofwaste material, for example an oleopholic waste material.

Examples of waste materials with which the invention is concernedinclude such materials present in a sludge. Sludges are generated invarious industrial processes. For example, the cleaning of metal partsto remove grease may involve soaking the part in an organic solvent withthe result that the grease removed (i.e. the waste material) forms asludge with the organic solvent. Sludges may also be produced, forexample, from dye, ink, and paint industries in which paint, ink or dyeis dissolved in an organic solvent. The organic solvents may, bechlorinated solvents, e.g. trichloroethylene, perchloroethylene etc., oraromatic solvents, e.g. toluene. The sludges generally have no value.

Examples of other waste materials with which the invention is concernedinclude oil, tar or the like provided for example in the form of: oil(or tar) contaminated sand.

Problems can be encountered in the disposal of the above types of wastematerial to ensure that they do not adversely affect the environment.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate or mitigate theabove mentioned problems.

According to a first aspect of the present invention there is provided aprocess of the encapsulation of a waste material comprising providingthe waste material in association with a vaporizable liquid, admixingthe waste material/liquid composition with an absorbent particulatematerial, and heating the admixture to remove the solvent.

According to a second aspect of the invention there is providedapparatus for encapsulating waste material comprising a mixer, means forsupplying a composition of the waste material and a vaporizable liquidto the mixer, and heating means for heating the content of the mixer toremove said liquid.

The preferred particulate material for use in the invention is Fly Ash(available as a waste-product from coal-burning power stations) althoughother absorbent particulate materials may be used e.g. Kieselguhr orlime.

Preferably, the particulate material has a particle size of 10-40microns. An example of such a material is so called mechanical Fly Ash.

Ideally the waste material is substantially completely disolved in thevapourizable liquid which will generally be an organic solvent.

The organic solvent may, for example, be an aliphatic or aromaticsolvent. The solvent may be a chlorinated solvent, e.g. a perchlorinatedsolvent. Examples of solvents include trichloroethylene,perchloroethylene, acetone and toluene.

The presence of the vapourizable liquid (preferably an organic solvent)in the sludge is an important feature of the invention. We have foundthat the liquid allows the waste material to be transported into theparticulate material but that subsequent removal of the liquid byvapourization allows the waste material to remain firmly bound withinthe particulate material. Thus, the waste material will not "leach" outof the particulate material which may therefore simply be disposed of,for example in a landfill site. However, the particulate material may beput to more beneficial use, for example as a filler in constructionmaterials, e.g. tarmac. A particularly beneficial use of the material isin the manufacture of breeze blocks. Thus, the present invention enablestwo (normally) waste materials (e.g. Fly Ash and waste material beingtreated) to be converted into a product which has commercial value.

Waste material to be treated by the method of the invention willgenerally, but not necessarily, be oleophilic materials and may berelatively viscous materials (e.g. oils greases etc.). The wastematerial may come from a variety of sources, examples of which are givenbelow.

In one embodiment of the invention, the waste material may be in theform of a sludge or slurry which may or may not incorporate a relativelyminor proportion of an organic solvent.

Generally, sludges to be treated in the method of the invention will bewaste from a process in which the waste material (e.g. tar, oil, grease,ink, dye or paint) is dissolved, disposed or otherwise formulated withan organic solvent. It is however also possible for the presentinvention to be applied to the treatment of aqueous based sludges. Suchaqueous based sludges will be obtained, for example, in the digestion ofgrease by caustic soda. To treat the aqueous sludge, water is initiallyremoved (e.g. using membrane technology) and an organic solvent may beadded to "dissolve" the grease.

Irrespective of the type of sludge, it will generally be admixed with anexcess by volume of the vaporizable liquid under conditions whichpromote substantially complete disolution of the waste material andensure that there are no agglommerates or lumps of sludge. Typically thevolume of vaporizing liquid used will be up to 10 times that of thesludge although it will be appreciated that use of excessive amounts ofsolvents involves unnecessary expense, not least because of heatingcosts for vaporizing the solvent. Usually the volume of vapourisableliquid will be 1 to 5 times that of the sludge.

In a further embodiment, the invention may be applied to the treatmentof oil or tar contaminated sand. In this case, the contaminated sand maybe treated with the vaporizable liquid to break down the agglomeratedstructure and form a dispersion of the sand particles in the solvent inwhich the tar or oil may be dissolved. Sufficient vaporizable liquid maybe used to give a dispersion in the form of a slurry. Typically, thecontaminated sand is mixed with vaporizable liquid in a volume ratio ofsolvent to sand of up to 10:1, more preferably 1:1 to 5:1. Afteradmixture with the absorbent particulate material (e.g. Fly Ash) andremoval of the liquid the resulting product is an admixture of the sandand the particulate material in which the tar or oil is encapsulated.

It will be appreciated from the foregoing description that the inventionis applicable to the encapsulation of a wide variety of waste materials.The fundamental step is the treatment of the waste material to beencapsulated with a vaporizable liquid (generally using a volume ratioof up to 10:1, e.g. 1:1 to 5:1) which `transports` the waste materialinto the particulate material in which waste material is encapsulatedafter vaporization of solvent.

Preferably the volume ratio of particulate material: (waste material andvaporizable liquid) which are mixed together is greater than 1:1 and mayfor example be up to 10:1. Typically the ratio will be in the range 3:1to 6:1.

The mixing of the waste material/liquid composition and the particulatematerial is preferably effected in a rotary mixer comprising acylindrical drum with a helix formed on its inner surface. The drum maybe rotated about its longitudinal axis in one direction to mix thecontents thereof, and rotated in the other direction to pass thecontents for discharge from one end of the drum. The heating of themixture may conveniently be effected by a hot air circulation heaterpositioned proximate the drum axis.

Typically mixing will be effected for 30 minutes to 2 hours. Thetemperature to which the mixture is heated will depend on the boilingpoint of the liquid but will typically be in the range 40° to 90° C. Forexample, use of trichloroethylene as the liquid will require atemperature of 80°-87° C. whereas for acetone the temperature will be40°-50°.

BRIEF DESCRIPTION OF THE DRAWING

A specific embodiment of the present invention will now be described byway of example only with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic view of an apparatus according to the presentinvention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

As shown in the drawing, there is illustrated a sludge treatmentapparatus comprising a rotary mixer 1 having in inlet 2, a particulatematerial hopper 3, a heater 4, a solvent collection tank 5, and acontainer 6 for the final product.

The mixer 1 has a rotatable cylindrical drum provided on its innersurface with a helix 8. The outer surface of drum 7 rests on rollers 9by means of which the drum may be rotated. One end of the drum 7 isclosed, at which end the inlet 2 and particulate material hopper 3 aresituated. A scraper blade 10 is provided adjacent the other, open end ofthe drum 7 to scrape material from the drum sides. The heater 4 extendswithin the drum close to the longitudinal axis thereof.

Sludge to be treated will be passed along a line 11 into which isintroduced solvent from a solvent distillation unit 12. The mixture isfed by a diaphragm pump 13 to the inlet 2 so as to be introduced intodrum 7 in which mixing is effected to dissolve the sludge.

The particulate material hopper 3 will (in use of the apparatus) becharged with, for example, mechanical Fly Ash. Within the hopper 3 is aregulator valve 14 though which the particulate material is fed tohopper outlet 15 (located proximate sludge inlet 2). Fly Ash from hopper3 is introduced into drum 7 once the sludge has dissolved.

During operation of the process (described more fully below) solventwill be evaporated and collected in the solvent collection tank 5 (inwhich condensation is assisted by coils 16). Solvent may be returnedalong a line 17 (via a pump 18) to the distillation plant 12 forpurifying the solvent. Purified solvent from plant 12 may be fed intosludge line 11 to "dilute" the incoming sludge.

During operation of the process the drum 7 is rotated by the rollers 9.This rotation of the drum is carried out in a direction which permitsthe helix to effect mixing without conveying the contents out of theopen end of the drum.

The relative proportion of Fly Ash, waste material and solvent areselected so as to ensure complete encapsulation of the waste. Therelative amounts required may be determined by laboratory scaleexperiments. Generally the final mix will have the consistency of a wetslurry.

In the next stage, the heater 4 is operated to increase the temperaturewithin the drum to a level at which the solvent is evaporated from theparticulate material. Obviously, the particular temperature requiredwithin the drum will depend on the solvent which was present in theoriginal sludge. Solvent expelled from the particulate material iscollected in tank 5 for recycling to distillation plant 19 as describedpreviously.

When all solvent has been evaporated, the rotational direction of drum 7is reversed so that the treated particulate material is fed along thedrum and collected in the receptacle 6. During this operation, scraperblade 10 serves to remove material adhering to the inside of the drum.

The collected powder may be used as a filler for building materials.

EXAMPLES

The invention is illustrated by the following non-limiting examples.

Example 1

A tar/sand mixture obtained from tar ponds in Canada was mixed withacetone in a volume ratio of acetone:sand of 2:1. Mixing was effectedwith heating so as to dissolve the tar in the acetone. The resultingcomposition was admixed with 4 parts by volume of mechanical Fly Ashusing the apparatus illustrated in the drawing and heated at 40°-50° C.for 1 hour.

The product was a dry powder (admixture of sand and Fly Ash containingencapsulated tar) which could be used as a building material (e.g. inthe manufacture of breeze blocks or finished cement material).

The leachability of the tar from the Fly Ash was tested and found to beacceptable under Canadian Government Standards.

Example 2

A paint sludge containing about 2% of organic solvent was mixed withtrichloroethylene (TCE) in a volume ratio of TCE:sludge of 2:1. Mixingwas effected until the paint was in solution.

The resulting composition was mixed with 4 parts by volume of mechanicalFly Ash and the mixture heated at 80° C. to 87° C. to remove solvent.

The product was a dry powder. Leachability was found to be acceptablefor present landfill legislation in the U.K.

This Example could also be repeated with ink-, dye-, grease- oroil-based sludges.

Example 3

An aqueous based sludge which contained lubricants and protectivegreases and which was produced by the cleaning of car bodies wasobtained from a car assembly plant. The sludge was substantiallydewatered using membrane separation to give a waste material (i.e.lubricant and grease) containing about 10% water.

Two parts by volume of trichloroethylene were thoroughly mixed with 1part of volume of the waste material until the lubricants and greaseshad dissolved. Four parts by volume of mechanical Fly Ash were thenadded and mixing effected in the apparatus shown in the drawing and themixture was heated at 80° C. to 87° C. to vaporize the solvent.

The product was a dry powder which was acceptable for landfill purposes,the powder being non-leaching to U.K. Standards.

I claim:
 1. A process for the encapsulation of an oleophilic wastematerial, said process comprising:providing the waste material inassociation with an organic vaporizable liquid; admixing the wastematerial/liquid composition with an absorbent particulate material ofparticle size 10-40 microns selected from the group consisting of flyash and kieselguhr; and heating the admixture to remove the organicvaporizable liquid.
 2. A process as claimed in claim 1 wherein theparticulate material is mechanical Fly Ash.
 3. A process as claimed inclaim 1, wherein the oleophilic material is substantially completelydissolved in the vapourisable liquid.
 4. A process as claimed in claim 1wherein the ratio by volume of the vapourisable liquid to the wastematerial is less than 10:1.
 5. A process as claimed in claim 4 whereinsaid ratio is 1:1 to 5:1.
 6. A process as claimed in claim 1, whereinthe vapourisable liquid is an organic solvent.
 7. A process as claimedin claim 6, wherein the solvent is an aliphatic or aromatic solvent. 8.A process as claimed in claim 6, wherein the solvent is a chlorinatedsolvent.
 9. A process as claimed in claim 8, wherein the solvent istrichloroethylene or perchloroethylene.
 10. A process as claimed inclaim 6 wherein the solvent is acetone or toluene.
 11. A process asclaimed in claim 1 wherein the volume ratio of particulate material:waste material and solvent is greater than 1:1.
 12. A process as claimedin claim 11 wherein said ratio is up to 10:1.
 13. A process as claimedin claim 12 wherein said ratio is 3:1 to 6:1.
 14. A process as claimedin claim 1 wherein the admixing of the waste material, liquid and theparticulate material is effected in a rotary cylindrical drum having anaxis an formed with a helix on its inner surface.
 15. A process asclaimed in claim 14 wherein the heating of the mixture to remove solventis effected by a hot air circulation heater positioned proximate thedrum axis.
 16. Apparatus for encapsulating waste material comprising:arotary mixer comprising a rotatable cylinder drum having an axis and ahelix formed on an inner surface of said drum; means for supplying acomposition of the waste material and a vaporizable liquid to the mixer;means for supplying an absorbent particulate material to the mixer; andheating means for heating the content of the mixer to remove saidliquid.
 17. An apparatus as claimed in claim 16 wherein the heatingmeans comprises a hot air circulation heater positioned proximate thedrum axis.